Did a deep freeze spur our ancestors to get cooking? The discovery that the oldest pots in the world were made in China around the time of the Last Glacial Maximum suggests that might be the case.

Hundreds of fragments of pottery have been found since the 1960s in Xianrendong cave in south-east China.

Ofer Bar-Yosef of Harvard University and colleagues excavated the cave again in 2009 and, for the first time, used radiocarbon dating to work out the age of the layers where the pottery shards were found. The oldest ones turned out to be between 19,000 and 20,000 years old.

That is thousands of years before people began farming some 12,000 years ago – suggesting that the pots were made by hunter-gatherers, which is contrary to previous thinking. “The making of pottery is not necessarily related to agriculture,” says Bar-Yosef.

A pottery-agriculture link is, eg, that pottery is more necessary if one wants to store grain than if one wants to conserve hunting quarry, which is more difficult to conserve.

Also, Ice Age hunter-gatherers were often pedestrian nomads. Pottery fits better in a sedentary lifestyle of an agricultural village than with nomads, probably preferring light bags.

Bar-Yosef thinks the shards are the remains of crude pots and bowls, probably about 20 centimetres across. “They were poorly fired and easily breakable,” he says. Their outer surfaces carry scorch marks and small amounts of soot, so Bar-Yosef thinks they were used for cooking.

His dating data helps to locate the oldest potters, but humans had been manipulating clay into figurines for many years by then. The Venus of Dolní Věstonice, a small statuette of a naked woman found in what is now the Czech Republic is estimated to be about 30,000 years old.

What prompted Chinese hunter-gatherers to start cooking food 20,000 years ago? Bar-Yosef points out that, at the time, Earth was in the clutches of the Last Glacial Maximum, the height of the last ice age.

The extreme cold would have caused food shortages. Cooked food yields more energy than raw food, so throwing their meals on the fire could have helped people to survive. It takes some form of stress for species to undergo major changes, says Bar-Yosef.

A later cold period, the Younger Dryas starting about 12,800 years ago, could have forced people to start farming (Current Anthropology, DOI: 10.1086/659784). Because much of Eurasia was colonised by then, people couldn’t escape food shortages by moving to a new area. The only option was to start growing crops.